Étude ultrastructurale des coiffes des racines de chêne (Quercus robur). I. Les pivots

Abstract

Three zones may be distinguished in rootcaps of orthogeotropic taproots of oak seedlings.(1) The meristematic zone: cells have no distinctive characteristics except that they always have small rounded vacuoles.(2) The statocytes have amyloplastids accumulating in the lower cell portion. The nucleus is near the upper end. Unlike the herbaceous species studied, these cells have large central vacuoles. This may be a characteristic of woody species. This hypothesis is discussed.After a 90 or 135° rotation in a vertical plane, amyloplastids become progressively concentrated in the new lower end of the statocyte. Orientation of the endoplasmic reticulum also changes, and the vacuolar system is reorganized. At room temperature root curvature begins to appear more than 2 h after the rotation.(3) The outside cell layers are composed of mucilage secreting cells with dictyosomes producing large vesicles containing polysaccharides. These accumulate in the periplasmic area. A strong inosine diphosphatase activity is shown in the vesicles.